1. Field of the Invention
The present invention relates to a method of extrusion forming ceramic material, particularly suitable for extrusion forming of honeycomb ceramic structural body and an apparatus for use in the method.
2. Related Art Statement
Hitherto there have been made use of a ceramic batch of powder ceramic low material mixed with forming aids consisting of binding agent such as methyl cellulose or the like, plasticizer and lubricants for forming a ceramic honeycomb structural body. In forming process of such a ceramic batch there is a correlation between the temperature and hardness of the ceramic batch. The correlation is effected by the kind or amount of methyl cellulose or a combination with other forming aids, but it is generally depicted as shown in FIG. 3.
In a case of extrusion forming by use of such a ceramic batch having aforementioned characteristics there are disadvantages that when the temperature of the ceramic batch increases higher than the gelling temperature thereof, the hardness of the ceramic batch abruptly increases and also when the distribution of hardness of the ceramic batch is not uniform, defects are intended to occur in the honeycomb structural body to be formed.
Thus, according to the prior art, a test piece of about 50 mm thickness is taken from a ceramic batch at the outlet of an auger machine (downstream to a forming column ring) and instantaneously a rod shaped thermometer is inserted into the test piece to measure the temperature of the ceramic batch and at the same time the hardness of the ceramic batch of the test piece is measured by means of a penetrator. Then, an operator controls flow rate of cooling water for cooling the auger machine by hand according to the results of measurements.
As an alternative for saving handling by operator, Japanese Patent Application Laid-open
Publication No. 62-259805 discloses a method of controlling rotating speed of screw members of a pug portion and an auger portion of a vacuum pug mill according to a temperature difference between a temperature measured at an inlet portion of the pug portion and a temperature of a porous plate measured at an outlet of the pug portion.
However, in the method disclosed in the aforementioned Japanese Patent Application Laid-open Publication No. 62-259805, the temperature of the ceramic batch is presumed from the temperature of the porous plate arranged at the outlet of the pug portion and is not actually measured just before the ceramic batch is extruded from the pug portion. Consequently, the operation of the vacuum pug mill is not exactly and accurately controlled so that the kneaded ceramic batch is not satisfied for extruding by means of a plunger molding machine.